Semiconductor device

ABSTRACT

Semiconductor devices and fabrication methods are provided. In a semiconductor device, a semiconductor substrate includes a first electrode layer having a top surface coplanar with a top surface of the semiconductor substrate. A sacrificial layer is formed on the semiconductor substrate and the first electrode layer. A first mask layer made of a conductive material is formed on the sacrificial layer. The first mask layer and the sacrificial layer are etched until a surface of the first electrode layer is exposed to form openings through the first mask layer and the sacrificial layer. A cleaning process is performed to remove etch byproducts adhered to a surface of the first mask layer and adhered to sidewalls and bottom surfaces of the openings. Conductive plugs are formed in the openings after the cleaning process.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the priority of Chinese Patent Application No.201410027719.4 filed on Jan. 21, 2014, the entire content of which isincorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates to the field of semiconductor technology,more particularly, relates to semiconductor devices and fabricationmethods.

BACKGROUND

A Micro-Electro Mechanical System (MEMS) is an integrated device capableof obtaining information, processing information, and performingoperations. Sensors embedded in an MEMS system are able to sense outsideinformation such as pressure, position, speed, acceleration, magneticfield, temperature, and humidity, and to convert the sensed informationto electrical signals. The electrical signals can then be processed inthe MEMS. A pressure sensor is a device capable of converting pressuresignals to electrical signals.

A capacitive pressure sensor is one of the conventional pressuresensors. A conventional capacitive pressure sensor includes: asubstrate; a first electrode layer on the substrate; and a secondelectrode layer on top of the substrate and the first electrode layer. Acavity is formed between the first electrode layer and the secondelectrode layer and isolates the first electrode layer from the secondelectrode layer.

The first electrode layer, the second electrode layer, and the cavityform a capacitive structure. When the second electrode layer issubjected to pressure and undergoes a deformation, the distance betweenthe first electrode layer and the second electrode layer changes. Thecapacitance of the capacitive structure then changes accordingly. Sincethe pressure on the second electrode layer corresponds to thecapacitance of the capacitive structure, the pressure on the secondelectrode layer can be converted to an output signal of the structure.

However, the conventional pressure sensor lacks electrical stability.

BRIEF SUMMARY OF THE DISCLOSURE

One aspect or embodiment of the present disclosure provides asemiconductor fabrication method. A semiconductor substrate is providedto include a first electrode layer therein. The first electrode layerhas a top surface coplanar with a top surface of the semiconductorsubstrate. A sacrificial layer is formed on the semiconductor substrateand the first electrode layer. A first mask layer, made of a conductivematerial, is formed on the sacrificial layer. The first mask layer andthe sacrificial layer are etched until a surface of the first electrodelayer is exposed to form openings through the first mask layer and thesacrificial layer. A cleaning process is performed to remove etchbyproducts adhered to a surface of the first mask layer and adhered tosidewalls and bottom surfaces of the openings. Conductive plugs areformed in the openings after the cleaning process.

Another aspect or embodiment of the present disclosure provides asemiconductor device. The semiconductor device includes a semiconductorsubstrate, and a first electrode layer disposed in the semiconductorsubstrate. The first electrode layer has a top surface coplanar with atop surface of the semiconductor substrate. A sacrificial layer isdisposed on the semiconductor substrate and the first electrode layer. Afirst mask layer is disposed on the sacrificial layer. The first masklayer is made of a conductive material. Conductive plugs are formedthrough the first mask layer, through the sacrificial layer, and on asurface of the first electrode layer.

Other aspects or embodiments of the present disclosure can be understoodby those skilled in the art in light of the description, the claims, andthe drawings of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are merely examples for illustrative purposesaccording to various disclosed embodiments and are not intended to limitthe scope of the present disclosure.

FIG. 1 is a cross-section illustration of a conventional pressuresensor;

FIGS. 2-9 illustrate cross-section views of a semiconductor devicecorresponding to certain stages of an exemplary fabrication processconsistent with the disclosed embodiments; and

FIG. 10 illustrates an exemplary fabrication process of a semiconductordevice consistent with the disclosed embodiments.

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary embodiments of theinvention, which are illustrated in the accompanying drawings.Hereinafter, embodiments consistent with the disclosure will bedescribed with reference to drawings. Wherever possible, the samereference numbers will be used throughout the drawings to refer to thesame or like parts. It is apparent that the described embodiments aresome but not all of the embodiments of the present invention. Based onthe disclosed embodiment, persons of ordinary skill in the art mayderive other embodiments consistent with the present disclosure, all ofwhich are within the scope of the present invention.

Pressure sensors may lack electrical stability. FIG. 1 is across-section view of a conventional pressure sensor. The conventionalpressure sensor includes: a substrate 100, a first electrode layer 101on the substrate; and a second electrode layer 102 on the substrate 100and the first electrode layer 101. A cavity 103 is formed between thefirst electrode layer 101 and the second electrode layer 102. A firstconductive plug 104 and a second conductive plug 105 are formed betweenthe first electrode layer 101 and the second electrode layer 102. Thesecond conductive plug 105 and the second electrode layer 102 areelectrically isolated by an isolation layer. The first electrode layer101 under the second conductive plug 105 and the first conductive plug104 are electrically isolated. The sidewalls of the first conductiveplug 104 and the second conductive plug 105 are surrounded by aprotective layer 106, respectively. A second protective layer 107 islocated between the opposing layers of the second electrode layer 102and the first electrode layer 101.

The first conductive plug 104 and the second conductive plug 105 areconfigured to provide support for the second electrode layer 102overhanging above the first electrode layer 101. Further, voltages areapplied on the first electrode layer 101 and the second electrode layer102 to sense the capacitance variation of the capacitive structureformed by the first electrode layer 101, the second electrode layer 102,and the cavity 103. In addition, the first conductive plug 104 and thesecond conductive plug 105 are connected to the first electrode layer101, respectively. The first electrode layer 101 is connected to thefirst conductive plug 104 and electrically isolated from the firstelectrode layer 101 connected to the second conductive plug 105 by ahumidity-sensitive dielectric material. The electrically isolated firstelectrode layer 101 and humidity-sensitive dielectric material form ahumidity-sensitive capacitive sensor. By applying voltages on the firstconductive plug 104 and the second conductive plug 105, the capacitancevariation of the humidity-sensitive capacitance sensor formed by thefirst electrode 101 and the humidity-sensitive material can be obtained.Therefore, the humidity-sensitive capacitance sensor can sense pressureand humidity of the outside environment.

When fabricating the sensor shown in FIG. 1, a sacrificial layer isformed in the cavity 103. The second protective layer and the secondelectrode layer 102 are formed on the sacrificial layer. Later, thesacrificial layer is removed after the formation of the second electrodelayer 102. Since the first conductive plug 104 and the second conductiveplug 105 are formed in the sacrificial layer, the sacrificial layerneeds to be etched to form openings that are used to form the firstconductive plug 104 and the second conductive plug 105.

When forming openings in the sacrificial layer, a dielectric material,such as a silicon oxide, is often used as an etch mask. Due to thesufficiently low mechanical strength of the dielectric material and adesirable deep opening, the dielectric layer used as the etch mask isusually thick in order to ensure the mask pattern to stay stable duringan etch process. However, it has been found that, etch byproducts, e.g.,polymers, are prone to be formed from etching of the dielectric masklayer. The etch byproducts are adhered to the sidewalls of the masklayer, and brought into the openings by the etchant gases when etchingthe sacrificial layer. The etch byproducts then get adhered to thesidewalls and the bottoms of the openings. These etch byproducts canprovide the subsequently formed first conductive plug 104 and the secondconductive plug 105 with unstable electrical properties. The contactresistance between the first conductive plug 104 (and the secondconductive plug 105) and the first electrode layer 101 increasesaccordingly. Therefore, the sensors fabricated by this method may havedegraded performance and decreased stability.

When the mask layer is made of silicon dioxide and the sacrificial layerhas a thickness greater than 5000 Å (e.g., the depth of the openings aregreater than 5000 Å), a large amount of polymers can be formed on thesidewalls and bottoms of the openings. The polymers are normally removedby using regular wet cleaning process or dry cleaning process. However,for a sensor shown in FIG. 1, the thickness of the sacrificial layerneeds to be greater than 22000 Å (e.g., the depth of the openings aregreater than 22000 Å), which means a thicker layer of mask layer isneeded for the etch process. Since the amount of polymers formed fromthe etch process increases with the thickness of the mask layer, thebyproducts adhered to the sidewalls and bottoms of the openings areharder to remove.

Various embodiments provide a semiconductor device and fabricationmethod. For example, a first mask layer formed on the sacrificial layeris made of a conductive material. The first mask layer is also used asthe etch mask for the sacrificial layer. Since etching the conductivematerial does not generate any hard-to-remove etch byproducts adhered tothe etched surface, the sidewalls and bottoms of the openings in thesacrificial layer can be by cleaning processes after etching the firstmask layer. Better electrical stability of the conductive plugs cantherefore be ensured accordingly.

Further, since the first mask layer is made of a conductive layer, thefirst mask layer can be part of the semiconductor device after thedevice fabrication and does not need to be removed after the formationof the openings and the conductive plugs. Specifically, the first masklayer can be a second electrode layer. After the removal of thesacrificial layer, the first mask layer can be overhung above the firstelectrode layer. A pressure sensor can be formed by the first mask layerand the first electrode layer. Therefore, the fabrication process of thesemiconductor device can be simplified, and damages to the conductiveplugs can be reduced. The semiconductor device fabricated by this methodcan have desirable electrical stability.

FIG. 10 illustrates an exemplary fabrication process of a semiconductordevice; and FIGS. 2-9 are cross-section views of a semiconductor devicecorresponding to various stages during the exemplary fabricationprocess.

As shown in FIG. 10, at the beginning of the process, a substrate havinga first electrode layer on top and a sacrificial layer on the firstelectrode layer is provided (S101). FIG. 2 illustrates a correspondingcross-section view of the semiconductor structure.

As shown in FIG. 2, a substrate 200 is provided. The substrate 200 isconfigured to include a first electrode layer 201. Top surfaces of thefirst electrode layer 201 and the substrate 200 are coplanar with eachother. A sacrificial layer 202 is formed on the substrate 200 includingthe first electrode layer 201.

The substrate 200 may include: a semiconductor substrate 210,semiconductor components (not shown) on the semiconductor substrate 210or in the semiconductor substrate 210, and electrical interconnectstructures 211. Further, the substrate 200 may also include an isolationlayer 212 configured to provide electrical isolation between thesemiconductor components and the electrical interconnect structures 211.

The electrical interconnect structures 211 are configured to provideelectrical connections for the corresponding semiconductor components.

In one embodiment, the first electrode layer 201 and the isolation layer212 can form a humidity sensor. Further, the first electrode layer 201,a subsequently formed second electrode layer, and a cavity formedbetween the first electrode layer 201 and the second electrode layer canform a pressure sensor. Thus, the semiconductor device can be anintegrated device including a pressure sensor and a humidity sensor.

The semiconductor components can be any suitable CMOS devices. The CMOSdevices can further include transistors, memories, capacitors, and/orresistors.

The semiconductor substrate 210 can be made of silicon, SiGe, SiC,silicon-on-insulator (SOI), germanium-on-insulator (GOI), glass, and/orGroup III-V compounds (such as GaN or GaAs).

In one embodiment, the material of the isolation layer 212 can includehumidity-sensitive dielectric materials, such as polyimide. Theisolation layer 212 can also be used as the dielectric layer of thecapacitive humidity sensor.

In one embodiment, the substrate 200 can be a silicon substrate. Thesemiconductor components in the substrate 200 can be transistors (notshown). The top surface of the substrate 200 can include the top surfaceof the isolation layer 212. The first electrode layer 201 can be formedin the substrate 200; and the top surface of the first electrode layer201 can be coplanar with the top surface of the isolation layer 212.

In addition, the first electrode layer 201 can be a bottom electrode ofthe subsequently formed pressure sensor. The subsequently formed secondelectrode layer can be a top electrode of the pressure sensor. Thecavity subsequently formed between the first electrode layer 201 and thesecond electrode layer, the first electrode layer 201, and the secondelectrode layer can form the capacitive pressure sensor. By sensing thecapacitance variation of the capacitive pressure sensor, pressure of theoutside environment can be obtained.

The first electrode layer 201 can be made of conductive materials suchas Cu, W, and/or Al. In one embodiment, a portion of the isolation layer212 surrounding the first electrode layer 201 can be ahumidity-sensitive material. The first electrode layer 201 can beelectrically connected to the semiconductor components (not shown) viathe electrical interconnect structures 211.

Since a cavity can be formed between the subsequently formed secondelectrode layer and the first electrode layer 201, a pressure sensor canbe formed by the first electrode layer 201, the second electrode layer,and the cavity. Thus, before the formation of the second electrodelayer, the sacrificial layer 202 can be formed on the first electrodelayer 201. The sacrificial layer 202 can be configured to occupy thespace corresponding to the subsequently formed cavity. Later, after theformation of the second electrode, the sacrificial layer 202 can beremoved to form the cavity.

Since the thickness of the sacrificial layer 202 can determine thesubsequently formed distance between the first electrode layer 201 andthe second electrode layer, and the distance can further determine thecapacitance of the capacitive structure formed subsequently between thefirst electrode layer 201 and the second electrode layer. Thesacrificial layer 202 can be sufficiently thick to satisfy technicalrequirements for the capacitive structure. Specifically, the sacrificiallayer 202 can be 22000 Å in one embodiment.

The sacrificial layer 202 can be formed by using a chemical vapordeposition process or a physical vapor deposition process. The materialof the sacrificial layer 202 can differ from the materials of the firstelectrode layer 201, the subsequently formed first mask layer, and thesubsequently formed second mask layer, in order to ensure less damagesto the first electrode layer 201, the first mask layer, and the secondmask layer during the removal process of the sacrificial layer 202.

In one embodiment, the sacrificial layer 202 can be made of amorphouscarbon. The etchant gases used to etch the amorphous carbon can includeoxygen, and the chemical reaction between the oxygen and the amorphouscarbon can produce CO and/or CO₂. Therefore, solid byproducts can bereduced during the removal process of the amorphous carbon, anddesirable surface morphology of the first electrode layer 201 can beprovided after the etching of the sacrificial layer 202.

Returning to FIG. 10, a first mask layer on the sacrificial layer can beformed (S102). FIG. 3 illustrates a corresponding cross-section view ofthe semiconductor structure.

As shown in FIG. 3, a first mask layer 203 is formed over thesacrificial layer 202. The first mask layer 203 can be made of aconductive material.

In order to form conductive plugs on the surface of the first electrodelayer 201, openings are to be made in the sacrificial layer 202 toexpose portions of the first electrode layer 201. Thus, the first masklayer 203 can be formed on the sacrificial layer 202 to expose portionsof the first electrode layer corresponding to the positions of theopenings.

Since the openings are configured to later expose the first electrodelayer 201, the depths of the openings can be equal to the thickness ofthe sacrificial layer 202. That is, the thickness to be removed by asubsequent etching process can be equal to the thickness of thesacrificial layer 202. Because the thickness of the sacrificial layer202 can be sufficiently thick, the first mask layer 203 is required tohave high mechanical strength to ensure the patterns of the first masklayer 203 stay stable during the etching process of the sacrificiallayer 202.

Conventionally, the mask layer used to define the position and structureof the subsequently-formed openings can be made of dielectric materialswith limited mechanical strength. Since the sacrificial layer can besufficiently thick, the mask layer may also need to have a largethickness to protect the pattern of the mask layer from being damaged byover-thinning of the mask layer due to use of conventional dielectricmaterials for the mask layer. However, because large amount ofbyproducts (such as less-volatile polymers) can be generated whenetching the mask layer made of conventional dielectric materials, thebyproducts may gradually get adhered to the sidewalls and bottoms of theopenings during the etching process. Additionally, the amount ofbyproducts increases as the thickness of the mask layer increases.Consequently, when conductive plugs are formed in the openings, thebyproducts can cause large contact resistance between the conductiveplugs and the first electrode layer.

In one embodiment, to suppress the formation of the byproduct frometching of the first mask layer 203, the first mask layer 203 can bemade of a conductive material. The etching of the conductive materialcan produce only a small amount of byproducts, and the byproducts can beeasily removed to provide clean sidewalls and the bottoms of thesubsequently formed openings. Contact resistance between the conductiveplugs and the first electrode layer can be reduced accordingly.

In one embodiment, the first mask layer 203 can be made of Ti, TiN, TaN,and/or Al. Since the material of the first mask layer 203 is aconductive material, the first mask layer 203 can further be used as asecond electrode layer of the pressure sensor. That is, when theopenings are formed in the sacrificial layer 202, the first mask layeris not removed but used as the second electrode layer on the sacrificiallayer. Thus, the fabrication process can be simplified.

In addition, damages to the surface of the sacrificial layer 202 and thesidewalls and bottoms of the openings in the sacrificial layer 202caused by the removal of the first mask layer 203 can be avoided. In oneembodiment, the first mask layer 203 can be made of Ti. Ti has highmechanical strength and low resistivity and can be used as the secondelectrode layer of the pressure sensor.

Further, the thickness of the first mask layer 203 can be about 200 Å toabout 300 Å. Since the first mask layer 203 is made of a conductivematerial, the first mask layer 203 thus has high mechanical strength.That is, even if the first mask layer 203 is thin, the patterns and thethickness of the first mask layer 203 can stay stable when used as theetch mask for forming the openings. Also, when the first mask layer 203is thin, the amount of byproducts formed from etching the first masklayer 203 can be low. Thus, the low amount of byproducts further ensuresclean sidewalls and bottoms of the formed openings.

In one embodiment, to prevent the first mask layer 203 from peeling offduring the etching of the openings, a second mask layer 204 can beformed on the sacrificial layer 202 before forming the first mask layer203. The first mask layer 203 can be formed on the second mask layer204. The second mask layer 204 can improve the adhesion between thefirst mask layer 203 and the sacrificial layer 202.

The second mask layer 204 can be made of a dielectric layer. Thethickness of the second mask layer can be about 150 Å to about 250 Å.Since the second mask layer 204 can be used to bind the first mask layer203 with the sacrificial layer 202, the second mask layer 204 may bethin. Accordingly, the etching of the second mask layer 204 can onlyproduce a small amount of byproducts and thus may not affect theperformance of the semiconductor device.

In one embodiment, the second mask layer 204 can be made of Si₃N₄. TheSi₃N₄ can improve the adhesion between the first mask layer 203 and thesacrificial layer 202. Even if the Si₃N₄ layer is thin, the Si₃N₄ layercan still provide sufficient mechanical strength as an etch mask for thesubsequent etching of the sacrificial layer 202.

Additionally, the first mask layer 203 can be used as the secondelectrode layer of the pressure sensor, and can be kept after removingthe sacrificial layer to form a cavity. The second mask layer 204 formedbetween the first mask layer 203 and the sacrificial layer 202 canprevent damage on the surface of the first mask layer 203 opposing thefirst electrode layer 201 during the removal process of the sacrificiallayer 202. Thus, the surface of the second electrode layer can beprotected and electrical stability of the second electrode layer can beensured.

Returning to FIG. 10, after forming the first mask layer 203 on thesacrificial layer 202, a patterned layer is formed on the first masklayer to expose portions of the first mask layer corresponding to thefirst electrode layer (S103). FIG. 4 illustrates a correspondingcross-section view of the semiconductor structure.

As shown in FIG. 4, a patterned layer 205 is formed on the first masklayer 203 to expose portions of the first mask layer 203 correspondingto the first electrode layer 201.

The patterned layer 205 can be used as an etch mask for the subsequentetching of the first mask layer 203 and the second mask layer 204. Thepatterned layer 205 can also define the positions and structures of thesubsequently formed openings. Specifically, the patterned layer 205 canexpose portions of the first mask layer 203 corresponding to at leasttwo separate sub-electrodes of the first electrode layer 201. That is,the multiple openings subsequently formed in the sacrificial layer 202can expose at least two separate sub-electrodes of the first electrodelayer 201.

In one embodiment, the patterned layer 205 can be made of photoresist.The fabrication process of the patterned layer 205 may include:depositing a photoresist layer on the first mask layer 203, exposing andpatterning the photoresist layer, and developing the patternedphotoresist layer to expose portions of the first mask layer 203 to formthe patterned layer 205.

In other various embodiments, the patterned layer 205 can be formed byusing multiple patterning technology (such as self-aligned doublepatterning technology, self-aligned triple patterning process, or doubleexposure process), molecular self-assembly process, or nano-printingprocess, in order to reduce the dimension of the openings or to reducedistance between adjacent openings in a direction parallel to the topsurface of the substrate 200. As such, the patterned layer 205 can beformed to allow formation of smaller semiconductor devices.

Returning to FIG. 10, after forming the patterned layer 205 on the firstmask layer to expose portions of the first mask layer 203 correspondingto the first electrode layer 201, the patterned layer 205 is used as theetch mask for etching the first mask layer and the sacrificial layer toexpose the surface of the first electrode layer. Further, openings areformed in the first mask layer and the sacrificial layer (S104). FIG. 5illustrates a corresponding cross-section view of the semiconductorstructure.

As shown in FIG. 5, the patterned layer 205 (as shown in FIG. 4) can beused as the etch mask for the etching of the first mask layer 203 andthe sacrificial layer 202 until the surface of the first electrode layer201 is exposed to provide a sub-electrode 201 a. For example, openings206 can be formed in the first mask layer 203 and the sacrificial layer202 and on surface of separate sub-electrodes 201 a of the firstelectrode layer 201.

The number of openings 206 formed in the first mask layer 203 and thesacrificial layer 206 can be at least two to expose the surfaces of atleast two separate sub-electrodes 201 a of the first electrode layer201. Conductive plugs can be formed in the openings 206. The conductiveplugs can be used to apply voltages on the two separate sub-electrodesof the first electrode layer 201. By sensing the capacitance variationbetween the two sub-electrodes 201 a of the first electrode layer 201,humidity information of the outside environment can be obtained. Thatis, the two separate sub-electrodes 201 a of the first electrode layer201 exposed at the bottoms of the openings 206 can be the two electrodelayers of the humidity sensor. In one embodiment, the number of theopenings 206 can be at least two, and the bottoms of the two openings206 can expose at least two separate sub-electrodes 201 a of the firstelectrode layer 201.

The fabrication process of the openings 206 can include: a first etchingprocess using the patterned layer 205 as the etch mask for the etchingof the first mask layer 203 until the surface of the sacrificial layer202 is exposed. After the first etching process, a second etchingprocess can use the first mask layer 203 as the etch mask for theetching of the sacrificial layer 202 until the surface of the firstelectrode layer 201 is exposed.

For the first etching process, anisotropic dry etch can be used to etchthe first mask layer 203 and the second mask layer 204 to form patterns.In one embodiment, the first mask layer 203 can be made of Ti, and thesecond mask layer 204 can be made of Si₃N₄. The parameters of the firstetching process may include: a pressure of about 5 mTorr to about 15mTorr; a power of about 400 W to 600 about W; and etchant gasesincluding Cl₂, O₂, and HBr having a flow rate of Cl₂ of about 100 sccmto about 150 sccm, a flow rate of O₂ of about 1 to about 5 sccm, and aflow rate of HBr of about 100 sccm to about 150 sccm.

Since the first mask layer 203 can be made of a conductive layer, forexample, Ti. In one embodiment, the amount of the etch byproductsproduced from etching the first mask layer 203 can be sufficientlysmall. Also, since the first mask layer 203 can be sufficiently thin,the etching depth of the first mask layer 203 can be sufficientlyshallow. Accordingly, the amount of etch byproducts produced can besufficiently low.

In addition, the second mask layer 204 can be made of Si₃N₄, and thethickness can be about 150 Å to about 250 Å. Since the second mask layer204 can only be the adhesion layer between the first mask layer 203 andthe sacrificial layer 202, the second mask layer 204 can be thin. Theamount of etch byproducts produced from etching the second mask 204 canbe low. Also, the amount of byproducts produced can be lower than theamount of etch byproducts produced from etching SiO₂ or otheralternative dielectric materials as conventionally used.

For the second etching process, isotropic dry etch can be used to etchthe sacrificial layer 202 to form the openings 206. The first mask layer203 and the second mask layer 204 can be used as the etch mask. In oneembodiment, the sacrificial layer 202 can be made of amorphous carbon,with a thickness of about 22000 Å. The parameters of the second etchingprocess may include: a pressure of about 80 mTorr to about 120 mTorr; apower of about 200 W to about 400 W; and etchant gases of Ar and O₂,having a flow rate of Ar of about 30 sccm to about 80 sccm, and a flowrate of O₂ of about 200 sccm to about 300 sccm. O₂ can be used to reactwith the amorphous carbon for etching. Ar can be used as a carrier gasto transport and disperse O₂.

In one embodiment, after the first etching process, the surface of thepatterned layer 205 may be damaged and patterns may be distorted. Toensure the shapes and precise dimensions of the openings 206, thepatterned layer 205 can be removed after the first etching process whilebefore the second etching process. Thus, patterns of the patterned layer205 would not result any adverse impact on the second etching process.That is, only the first mask layer 203 and the second mask layer 204 canbe used as the etch masks for the second etching process.

Since the sacrificial layer 205 can be made of amorphous carbon, the COor CO₂ produced from the reaction between the amorphous carbon and O₂can be released. Thus, the amount of byproducts produced from etchingthe sacrificial layer 202 is considerably small. Meanwhile, since thefirst mask layer 203 and the second mask layer 204 can be sufficientlythin, the etching of the first mask layer 203 and the second mask layer204 can only produce a small amount of etch byproducts. In addition, theetching of the conductive first mask layer 203 may also produce a smallamount of etch products. Therefore, in the second etching process, theetch byproducts brought into the openings 206 and further adhered to thesidewalls and bottoms of the openings 206 can be small. Even if someetch byproducts are still attached in the openings 206, cleaning of thebyproducts can be considerably easy.

Returning to FIG. 10, after using the patterned layer 205 as the maskfor etching the first mask layer 203 and the sacrificial layer 202 andforming the openings 206, a cleaning process is performed to remove theetch byproducts adhered to the surface of the first mask layer and thesidewalls and bottoms of the openings (S105). FIG. 6 illustrates acorresponding cross-section view of the semiconductor structure.

As shown in FIG. 6, a cleaning process can be performed to remove theetch byproducts adhered to the surface of the first mask layer 203 andthe sidewalls and bottoms of the openings 206.

After the first etching process and the second etching process, sincethe amount of etch byproducts adhered to the sidewalls and bottoms ofthe openings 206 can be small, the etch byproducts are easily removed bycleaning. Thus, the contact resistance between the first electrode layerand the subsequently formed conductive plugs can be sufficiently small.Stable electrical properties of the semiconductor device can be ensuredaccordingly.

The cleaning process may include: performing a dry cleaning process onthe surface of the first mask layer 203, and the sidewalls and bottomsof openings 206. Further, after the dry cleaning process, a wet cleaningprocess can be performed on the surface of the first mask layer 203, andthe sidewalls and bottoms of openings 206.

The parameter of the dry cleaning process may include: a pressure ofabout 90 mTorr to about 100 mTorr; a power of about 200 W to about 400W; and etchant gases of Ar and O₂ having a flow rate of Ar of about 250sccm to about 350 sccm, and a flow rate of O₂ of about 10 sccm to about30 sccm.

Since the etchant gases used for the dry cleaning process can be thesame as the second etching process, the transition between the secondetching process and the dry cleaning process can be easy. In addition,it is not necessary to transport the substrate 200 along with the formedsemiconductor device from the etching chamber to the cleaning apparatus.Thus, contamination caused by transportation can be avoided. Further,since the amount of etch byproducts adhered to the sidewalls and bottomsof the openings 206 can be small, the etch byproducts can be cleaned bythe dry etching process easily.

Additionally, the parameters of the wet cleaning process may include: acleaning agent of ST-44, including diglycolamine (2-(2-Aminoethoxy)Ethanol) and butyrolactone (Butyrolactone); a cleaning temperature ofabout 50 to about 100 degrees Celsius for a cleaning time of about 50 toabout 80 minutes. The wet cleaning process can be further used to removean oxidation layer formed in previous fabrication processes. Forexample, oxidation layers may be formed on the first mask layer 203 andthe first electrode layer 201 in the previous first etching process, thesecond etching process, and the dry cleaning process. Thus, smallcontact resistance between the first electrode layer 201 and thesubsequently formed conductive plugs can be further ensured.

Returning to FIG. 10, after performing the cleaning process to removethe etch byproducts adhered to the surfaces of the first mask layer 203and sidewalls and bottoms of the openings 206, conductive plugs areformed in the openings (S106). FIG. 7 illustrates a correspondingcross-section view of the semiconductor structure.

As shown in FIG. 7, after the cleaning process, conductive plugs 207 areformed in the openings 206 (shown in FIG. 6).

The conductive plugs 207 can be made of Cu, W, and/or Al. The conductiveplugs 207 can be formed by using deposition, electroplating, and/orchemical plating. In one embodiment, the conductive plugs 207 can bemade of W. The fabrication process of conductive plugs 207 can includeforming a conductive film on the surface of the first mask layer 203,and the sidewalls and bottoms of the openings 206 to fill up theopenings 206. The conductive film is then planarized by using a chemicalmechanical polishing process until the surface of the first mask layer203 is exposed. Further, the conductive plugs 207 are formed from theconductive film in the openings 206. The formation process of theconductive film can be a physical deposition process or a chemicaldeposition process. In other various embodiments, if the conductiveplugs 207 are made of Cu, the conductive film can also be formed byusing copper electrochemical plating (ECP).

In one embodiment, in order to protect the surfaces of the conductiveplugs 207 during the subsequent removal process of the sacrificial layer202, a protective layer can be formed between the conductive plugs 207and the sacrificial layer 202. In one embodiment, the protective layercan be made of TiN or TaN. Before the formation of the conductive layer,the protective layer can be formed on the first mask layer 203, and thesidewalls and bottoms of the openings 206. After planarizing theconductive film, the chemical mechanical polishing process can be usedto planarize the protective layer until the surface of the first masklayer 203 is exposed. Thus, the protective layer can be formed.

Returning to FIG. 10, after forming the conductive plugs 207 in theopenings after the cleaning process, an etch process can be performed onthe first mask layer to expose a portion of the sacrificial layer andform through-holes in the first mask layer (S107). FIG. 8 illustrates acorresponding cross-section view of the semiconductor structure.

As shown in FIG. 8, after the formation of the conductive plugs 207, anetch process can be performed on the first mask layer 203 until thesacrificial layer 202 is exposed. Through-holes 208 can be formed in thefirst mask layer 203.

After the formation of the conductive plugs 207, the sacrificial layer202 can be removed, and a cavity can be formed between the first masklayer 203 and the first electrode layer 201, accordingly. In order toexpose the sacrificial layer 202, portions of the surface of thesacrificial layer 202 may need to be exposed and a subsequent isotropicetch can be used to remove the exposed sacrificial layer 202. The cavitycan thus be formed.

Since the bottoms of the through-holes 208 can expose portions of thesacrificial layer 202, the cavity between the first mask layer 203 andthe first electrode layer 201 can be formed by etching the portions ofthe sacrificial layer 202 exposed by the bottoms of the through-holes208. The through-holes 208 can be one or more. The through-holes canhave a cross-section, in a direction parallel to the top surface of thesubstrate 200. The cross-section can be circular, rectangular, and/orstripe-shaped, according to specific fabrication requirements.

To form the through-holes 208, a patterned photoresist layer can beformed on the first mask layer 203 to expose portions of the first mask203, and the exposed portions of the first mask 203 can correspond topositions of the through-holes 208. The photoresist layer can then beused as an etch mask to etch the first mask layer 203 and the secondmask layer 204, until the sacrificial layer 202 is exposed. Thethrough-holes can thus be formed. Further, the photoresist layer can beremoved after the etch process. The parameters for the etching processof the first mask layer 203 and the second mask layer 204 can be thesame as the parameters for the first etching process.

Returning to FIG. 10, after etching the first mask layer 203 to exposeportions of the sacrificial layer 202 and form through-holes 208, thesacrificial layer 202 can be removed by using an isotropic etch to forma cavity between the first electrode layer and the first mask layer(S108). FIG. 9 illustrates a corresponding cross-section view of thesemiconductor structure.

As shown in FIG. 9, an isotropic etching process can be performed on thesacrificial layer 202 exposed by the bottoms of the openings 208, andportions of the sacrificial layer 202 between the first mask layer 203and the first electrode layer 201 can be further removed. The cavity 209can thus be formed between the first mask layer 203 and the firstelectrode layer 201. The first mask layer 203 can be overhung above thefirst electrode layer 201.

After removing the sacrificial layer 202, the cavity 209 can be exposedto the outside such that the isolation layer 212 can also be exposed tothe outside. The isolation layer 212 can be made of humidity-sensitivedielectric layer, such that the dielectric constant of the isolationlayer 212 can vary with humidity. The capacitance variation between thetwo separate sub-electrodes of the first electrode layer 201 can besensed, and the humidity information of the environment can thus beobtained.

The sacrificial layer 202 can be etched by an isotropic etching process.Since the etch rate of the isotropic etching process is the same in alldirections, the surface of the sacrificial layer 202 can be exposed byetching in a direction towards the first electrode layer 201. Meanwhile,the sacrificial layer 202 under the first mask layer 203 can be removedby etching in a direction parallel to the top surface of the substrate200. Thus, the cavity 209 can be formed between the first electrodelayer 201 and the first mask layer 203.

In one embodiment, since the first mask layer 203 is made of aconductive material, the first mask layer 203 can be used as a secondelectrode layer of the pressure sensor after the formation of the cavity209.

In one embodiment, the sacrificial layer 202 can be made of amorphouscarbon. The sacrificial layer 202 can be etched by the isotropic etchingprocess. The parameters of the isotropic etching process can be: etchantgases of O₂ and Ar; a power of less than 100 W; a voltage of less than100 V; and a temperature of higher than 100 degree Celsius. In oneembodiment, O₂ can react with the amorphous carbon and form CO and/orCO₂. The formed CO and/or CO₂ can thus be released.

During the etching of the sacrificial layer 202, the second mask layer204 can protect the surface of the first mask layer 203 facing the firstelectrode layer 201 such that the surface of the first mask layer 203 isnot etched.

Since an isotropic dry etch can be used to expose the first electrodelayer 210 and form the through cavity between the first mask layer 203and the first electrode layer 201, some of the sacrificial layer 202surrounding the cavity 209 may not be etched. The un-etched portions ofthe sacrificial layer 202 can remain in the cavity 209 to providesupport for the overhanging first mask layer 203 above the firstelectrode layer 201 as shown in FIG. 9.

In one embodiment, the first mask layer formed on the sacrificial layercan be made of a conductive material. The first mask layer can be usedas the etch mask for the etching of the sacrificial layer. Since theetching of the conductive material does not produce hard-to-removebyproducts adhered to the etched surface, the sidewalls and bottoms ofthe openings can be easily cleaned by a cleaning process after theetching of the first mask layer. Thus, better electrical stability ofthe subsequently formed conductive plugs in the openings can be ensured.Further, since the first mask layer is made of a conductive material,the first mask can also be used as part of the semiconductor device.That is, the first mask layer is not removed after the formations of theopenings and the conductive plugs. Specifically, the first mask layercan be used as the second electrode layer. After the removal of thesacrificial layer, the first mask layer can be overhung above the firstelectrode layer, and the pressure sensor can be formed accordingly.Therefore, fabrication process of the semiconductor device can besimplified, and damage to the electronic plugs can be reduced.Accordingly, the semiconductor fabricated by using the method disclosedcan have better electrical stability.

Compared with a conventional pressure sensor, the present disclosure hasthe following advantages. For example, in the fabrication process of thepresent disclosure, the first mask layer formed on the surface of thesacrificial layer is a conductive material. The first mask layer is usedas a mask to etch the sacrificial layer. Since the etching of theconductive material does not produce hard-to-remove byproducts (e.g.,polymers), that are easily adhered to the etched surface, the innersidewalls and the bottoms of the opening formed in the sacrificial layercan be cleaned easily by the cleaning process following the etching ofthe first mask layer. Better electrical stability of the subsequentlyformed conductive plugs can therefore be ensured. Further, since thematerial of the first mask layer is electrically conductive, the firstmask layer can be part of the semiconductor device after the devicefabrication. The first mask layer is not removed after the formations ofthe openings and the conductive plugs. Specifically, the first masklayer can be used as the second electrode layer. After the sacrificiallayer is removed, the first mask layer can be overhung above the firstelectrode layer, forming a capacitive sensor. Therefore, fabricationprocess of the semiconductor device can be simplified. The damage to theconductive plugs by the fabrication process can also be reduced.Accordingly, the semiconductor devices formed by the fabrication methoddisclosed can have better electrical stability.

Further, the first mask layer can be made of Ti, TiN, TaN, and/or Al.Specifically, Ti has good conductivity and high mechanical strength. Ifthe first mask layer is formed of Ti, even a thin Ti layer, the patternsof the first mask layer can stay stable during the etching of thesacrificial layer. Moreover, the first mask layer is used as the secondelectrode layer and has low electrical resistivity. Therefore, theoperating current of the resultant semiconductor device can beincreased, and energy consumption can be reduced accordingly.

Further, before formation of the first mask layer, the second mask layercan be formed on the sacrificial layer. The first mask layer can then beformed on the second mask layer. The second mask layer can be used toprotect surface of the first mask layer facing the first electrodelayer. Thus, when the first mask layer is used as the second electrodelayer, the quality of the first mask layer can be ensured. In addition,since the second mask layer is covered by the first mask layer, and thefirst mask layer has high mechanical strength, the second mask layer canthus be thin. Therefore, the etch byproducts produced from the etchingof the second mask layer are desirably less and can be easily removed.The performance of the semiconductor device formed by the fabricationdisclosure can be ensured accordingly.

Furthermore, the cleaning process can include a dry cleaning process,followed by a wet cleaning process. Since there is only little etchbyproducts adhered to the sidewalls and the bottoms of the openings andthe byproducts can be easily removed, the sidewalls and the bottoms ofthe openings can be cleaned completely by using the dry cleaning processand the wet cleaning process. The conductive plugs formed in theopenings can therefore have good shapes and surfaces, and betterelectrical stability.

Moreover, the disclosed semiconductor devices can include two exemplarysensors. For example, the first electrode layer and the isolation layercan form a humidity sensor. In addition, the first electrode layer, asubsequently formed second electrode layer (i.e., the first mask layer),and a cavity formed between the first electrode layer and the secondelectrode layer can form a pressure sensor. Thus, the semiconductordevice can be an integrated device including a pressure sensor and ahumidity sensor.

Other embodiments of the disclosure will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the claims.

1.-14. (canceled)
 15. A semiconductor device, comprising: asemiconductor substrate; a first electrode layer disposed in thesemiconductor substrate, wherein the first electrode layer has a topsurface coplanar with a top surface of the semiconductor substrate; asacrificial layer on the semiconductor substrate and the first electrodelayer; a first mask layer on the sacrificial layer, wherein the firstmask layer is made of a conductive material; and conductive plugs formedthrough the first mask layer, through the sacrificial layer, and on asurface of the first electrode layer.
 16. The device according to claim15, further comprising a second mask layer disposed between the firstmask layer and the sacrificial layer.
 17. The device according to claim15, wherein: the sacrificial layer comprises a cavity under the firstmask layer between the first electrode layer and the first mask layer,and the first mask layer is overhung above the first electrode layer,and the first mask layer is used as a second electrode layer of apressure sensor.
 18. The device according to claim 15, wherein the firstmask layer is made of Ti, TiN, TaN, Al, or a combination thereof, andwherein the first mask layer has a thickness of about 200 Å to about 300Å.
 19. The device according to claim 15, wherein the substrate furtherincludes: a semiconductor substrate; semiconductor components on thesemiconductor substrate or in the semiconductor substrate; electricalinterconnect structures, wherein the first electrode layer iselectrically connected to the semiconductor components via theelectrical interconnect structures; and an isolation layer, configuredto provide electrical isolation between the semiconductor components andthe electrical interconnect structures.
 20. The device according toclaim 15, further including a humidity sensor comprising the isolationlayer and at least two separate sub-electrodes from the first electrodelayer, wherein the isolation layer includes a humidity-sensitivedielectric material.
 21. The device according to claim 15, wherein thesecond mask layer is made of Si₃N₄, with a thickness in a range of about150 Å to about 250 Å.
 22. The device according to claim 15, wherein: theconductive plugs are made of Cu, W, Al, or a combination thereof.